Updated October 18, 2026. Quick answer: Line 1 is your adjusted gross income, line 2 is your itemized deductions or standard deduction, and line 3 subtracts line 2 from line 1. You fill in all three columns: what the return showed, the change, and the corrected amount. The figures come from the return you are amending.
Read box by box from the IRS form text: Form W-2c boxes c to i and Form W-2c Notice to Employee.
What lines 1 to 3 ask for
The form’s captions are “Adjusted gross income.” (with a box to check “If a net operating loss (NOL) carryback is included, check here”), “Itemized deductions or standard deduction”, and “Subtract line 2 from line 1”. This page is part of the Form 1040-X walk-through, and the next lines are on the lines 4a to 5 page.
Line 1: adjusted gross income
The instructions say “Enter your adjusted gross income (AGI), which is the total of your income minus certain deductions (adjustments).” They add “Any change to the income or adjustments on the return you are amending will be reflected on this line.” How AGI is built on the return itself is explained at Form 1040 lines 9, 10 and 11.
A change here can ripple: “A change you make to your AGI can cause other amounts to increase or decrease.” The instructions list credits and deductions that can move with it and then say “If you change your AGI, refigure the items listed above (if applicable), and any other deduction or credit you are claiming that has a limit based on AGI.”
For wages, “Attach a copy of all additional or corrected Forms W-2 you received after you filed your original return.” For an IRA deduction change, “If changing from a deductible to a nondeductible IRA contribution, also complete and attach Form 8606”. Form 8606 is explained at Form 8606.
Line 2: itemized or standard deduction
For itemizers: “If you itemized your deductions, enter in column A the total from your original Schedule A or your deduction as previously adjusted by the IRS.” If you are switching or changing an amount, “attach a copy of the corrected Schedule A to this amended return.”
For the standard deduction: “If you are using the standard deduction, enter the amount for your filing status for the year you are amending.” The deduction on your original return is explained at Form 1040 line 12.
Line 3: subtract line 2 from line 1
The instructions have no separate paragraph for line 3, so the form’s caption is the guide. It is plain subtraction in each column. Computed illustration, not an IRS example: if column C of line 1 is $51,200 and column C of line 2 is $20,000 then column C of line 3 is $51,200 minus $20,000 and the computed result is $31,200.
Where the number comes from
Column A comes from your original return or the return as adjusted. The instructions say “See the tax return for the year you are amending to find the corresponding lines on your original return.” For column C, the rule is “Add the increase in column B to the amount in column A”. Computed illustration, not an IRS example: an AGI of $50,000 in column A and an increase of $1,200 in column B gives $51,200 in column C ($50,000 plus $1,200).
Where it goes next
Line 3 feeds line 5, whose caption is “Taxable income. Subtract the total of lines 4a and 4b from line 3.” That is covered on the lines 4a to 5 page.
Edition and line numbers
This page reads the December 2025 revision of Form 1040-X, Amended U.S. Individual Income Tax Return, and its December 2025 instructions, the current files irs.gov served on 2026-10-18. Form 1040-X is not tied to one tax year: it amends the return year you enter at the top. The form’s own header says “Attach a completed Form 1040, 1040-SR, or 1040-NR, with your changes, for the return year entered below”. The instructions add “These instructions can be used with the December 2025 and later revisions of Form 1040-X, unless later instructions state otherwise.” Check the revision date printed on the form you are filling in and the return year you are amending, and use the line numbers on that form.
Common mistakes
- Changing AGI and stopping there. The instructions say “If you change your AGI, refigure the items listed above (if applicable), and any other deduction or credit you are claiming that has a limit based on AGI.”
- Using another year’s standard deduction. The instructions say “enter the amount for your filing status for the year you are amending.”
- Leaving a line blank because it did not change. The instructions say “For any item you don’t change, enter the amount from column A in column C.”
Related: Form 1040 lines 9, 10 and 11, Form 1040 line 12, Form 8606, and Form 1040.
Sources
- Instructions for Form 1040-X, Amended U.S. Individual Income Tax Return (Rev. December 2025): https://www.irs.gov/pub/irs-pdf/i1040x.pdf
- Form 1040-X, Amended U.S. Individual Income Tax Return (Rev. December 2025): https://www.irs.gov/pub/irs-pdf/f1040x.pdf
Read from the IRS documents linked above on October 18, 2026. General information, not tax advice. Your own facts decide the outcome, and a preparer, the account provider or the IRS is the right place to confirm anything consequential.